1. Field of the Invention
The present invention relates to a ceramic electronic device and a method of production of the same.
2. Description of the Related Art
As one method for producing a capacitor, piezoelectric device, or other ceramic electronic device, there is known the method of forming a ceramic coating in a sheet on a substrate by the doctor blade method to obtain a green sheet and forming electrode paste on top of this by screen printing. In this case, the ceramic coating includes ceramic powder, an organic binder, a plasticizer, a solvent, etc., while the electrode paste includes palladium, silver, nickel, or other conductive particles.
When desiring to obtain a multilayer structure, green sheets formed with the electrode paste layers are stacked to the desired multilayer structure and then cut by a press to obtain ceramic green chips. The thus obtained ceramic green chips are processed to remove the binder, then fired at 1000° C. to 1400° C. Silver, silver-palladium, nickel, copper, or other terminal electrodes are then formed on the obtained fired bodies to obtain the ceramic electronic devices.
In the above method of production, when producing for example a multilayer ceramic capacitor, to reduce the size and increase the capacity, the technique is adopted of reducing the thickness of each ceramic coating layer and increasing the number of layers. For example, multilayer ceramic capacitors are being developed having over 800 ceramic coating layers with thicknesses of about 3 μm.
In producing a ceramic electronic device such as a multilayer ceramic capacitor, however, when forming an internal electrode, the general practice in the past has been to coat a ceramic coating on the surface of a tape-like substrate having flexibility to form the ceramic coating layer, then print an internal electrode paste. The substrate has been made of polyethylene terephthalate (PET) film etc.
The ceramic coating used is obtained by mixing an acrylic resin or butyral resin or other organic binder, an organic solvent, a plasticizer, and a ceramic powder.
The internal electrode paste is prepared using a resin serving as an organic binder dissolved in an organic solvent as a vehicle, dispersing in the vehicle an Ag, Pd, Ni, Cu, or other conductive metal powder, and, in some cases, adding a diluent for adjusting the viscosity.
As the organic solvent in the vehicle, terpineol, methyl ethyl ketone, etc. is used. As the binder, ethyl cellulose, nitrocellulose, or another cellulose-based resin or butyl methacrylate, methyl methacrylate, or another acrylic-based resin is used. Further, as the diluent, an aromatic hydrocarbon, a fatty acid hydrocarbon, etc. is used.
When printing an internal electrode paste of such a composition on a ceramic coating layer coated on a substrate in accordance with the conventional method of production, however, the terpineol, methyl ethyl ketone, or other organic solvent contained in the internal electrode paste ends up dissolving the acrylic resin, butyral resin, or other organic binder contained in the ceramic coating layer. This phenomenon is called “sheet attack”.
If sheet attack occurs, it becomes difficult to peel off the ceramic coating layer from the substrate. Further, sometimes holes or wrinkles occur in the ceramic coating layer. If using such a ceramic coating layer to produce a multilayer ceramic capacitor, short-circuit defects where internal electrodes become connected will arise, withstand voltage defects will arise, the targeted electrostatic capacity will no longer be able to be obtained, or other critical defects are liable to occur.
As a means to avoid this problem, there is the method of printing an internal electrode directly on the substrate, coating a ceramic paste over this to form a ceramic coating layer, then peeling off the ceramic coating layer together with the internal electrode from the surface of the substrate (for example, see Japanese Patent No. 2136761).
With this method, however, the adhesion of the internal electrode and ceramic coating layer with respect to the substrate becomes stronger, so it becomes extremely difficult to peel off the ceramic coating layer without damage (holes, wrinkles, tears, etc.)
It may also be considered to coat the surface of a substrate with an agent for facilitating peeling (hereinafter called a “peeling agent”) in advance and form the internal electrode and ceramic coating layer on the surface of the peeling agent. In this case, the difficulty of peeling can probably be avoided.
When printing an internal electrode on the surface; of a peeling agent, however, since the affinity between the two is low, the internal electrode is subjected to an agglomerating action due to the surface tension, the shape of the pattern of internal electrode ends up being ruined, and the desired characteristics can no longer be obtained.